Protective means for mercury arc devices



Sept 17 193:5, D, Q, PRHNCE ZJIMSMQH PROTECTIVE MEANS FOR MERCURY ARC DEVICES Original Filed Aug. 12, 1930 Inventor: David C Prince,

His Attorne g Patented Sept. 17, 1935 UNITED STATES PATENT OFFICE PROTECTIVE MEANS FOR MERCURY ARC DEVICES David 0. Prince, Swarthmore, Pa., assignor to General Electric Company, a corporation of New York 1935, Serial No. 18,998

10 Claims.

This application is a division of my copending application, Serial No. 474,841, filed August 12, 1930, assigned to the same assignee as the present application.

My invention relates to electric systems wherein power is transmitted between direct and alternating current circuits by means of vapor electric devices such as mercury arc rectifiers and has for its principal object the provision 1 of improved apparatus whereby the systems are protected against electrical disturbance and damage caused by are back in the vapor electric devices.

Difiiculties have been encountered heretofore in the operation of vapor electric devices of the mercury arc rectifier type due to the occurrence of arc-back between negatively and positively charged anodes, or between other parts of these devices. The causes of arc-back have been obscure and noentirely satisfactory means have been provided heretofore for limiting to a negligible amount, or for preventing entirely, the damage thereby occasioned to transformer windings and other rectifier apparatus. In accordance with my invention this difiiculty is avoided by the provision of means responsive to the reverse current accompanying arc back for impressing a potential of such value on control electrodes associated with the anodes of the rectifier that, on occurrence of arc back, the flow of current therein is prevented.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, the single figure thereof is a diagram illustrating a rectifier system embodying the invention.

In the system shown in the figure, power is transmitted between a direct current circuit I and an alternating current circuit ll through a main transformer l2 having primary windings l3 and secondary windings l4, and a vapor electric device l5. This device in the present embodiment of the invention is a. rectifier comprising an evacuated vessel 16, only the lower part of which is shown in the figure, a mercury cathode anodes l8 and control electrodes l9 associated therewith.

Reverse current flowing upon occurrence of arc-back is utilized to operate a switch 32 which comprises high speed circuit breaker means arranged to open the direct current circuit I0 and simultaneously to operate relay means for impressing a suit-able negative potential on the control electrodes I9. The control and operating aparatus of the circuit breaker portion of switch 32 includes a holding magnet 33 which is provided with an armature 34 and with a holding coil 35 arranged to be energized through a suitable circuit 36, a resistor 31, and a switch 38. The armature 34 is mounted on a member 39 which is pivoted at 40 and is coupled to one of the main contact members 4| of the switch through a member 42. This member is biased to the position shown in the figure by a spring 43 and is arranged to move the armature 34 into engagement with holding magnet 33 in response to energization of a closing coil 44 shown as connected to the circuit 36 through a switch 45. The holding magnet 33 is provided with another coil 46, connected in series with a coil 4'! arranged to be energized by reverse current flowing in the direct current circuit I0. The various features of the circuit breaker portion of switch 32 are more fully disclosed in a Reissue Letters Patent to J. F. Tritle, No. 15,441, August 29, 1922.

The relay means operated by the above described circuit breaker portion of switch 32 com-- prises relay contacts 48, 49 and a relay contact member 59 connected to member 42. Contacts 48 and 49 are respectively adapted to connect current sources 5|, 52 between the cathode I! and the control electrodes l9. These current sources are so arranged that when the switch 32 operates to close contact 48 a potential positive with respect to the cathode is impressed through grid resistors 24 on the control electrodes I9, and when this switch operates to close contacts 49 the potential impressed on the control electrodes is negative with respect to the cathode. The switch 32 is so arranged that when the main contact members 4| are closed, to con-- nect the rectifier to the direct current circuit It], the relay contacts 48 are also closed, to connect current source 5| between the cathode I1 and control electrode l9, and that when the contacts 4| are open, to disconnect the rectifier, the relay contacts 49 are closed to connect current source 52 between the cathode and the control electrodes.

In the operation of the system, main switch contacts 4| are normally maintained in closed position by the flux produced in magnet 33 by holding coil 35. At the same time, the relay contacts 48 remain closed and a positive potential of any desired value, as required in normal operation, is thereby impressed on the control electrodes I!) by current source 5|. Upon 00- 55- currence of arc-back affecting one or more of the anodes the accompanying reversal of current in circuit 10 induces a current in coil 41. This induced current in coil 41 flows also in coil 46 connected in series therewith, the magnetic flux of the holding magnet 33 is shifted from the armature 34 to the iron core of the series coil 46 in a well known manner, and the switch contacts 4| are opened by the spring 43, thereby preventing power from the direct current net work from concentrating on the anode which is arcing back. It is known that the speed of a circuit breaker of the type above described is such that the circuit It] may be opened in less than one cycle of the alternating supply voltage of the rectifier. Simultaneously with the opening of the direct current circuit 10 at contacts 4| by switch 32, the contacts 49 are closed and a negative potential is impressed on the control electrodes I9 by current source 52. This negative potential causes the anodes to cease carrying current in succession, so that within one cycle, the flow of energy from the alternating current circuit ll into the short circuit which constitutes the arc-back is also interrupted and the rectifier is ready to resume operation as soon as the auxiliary arc usually provided is started and the switch 32 reset in closed position.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an are discharge device having a cathode, a plurality of P j anodes and control electrodes therefor, and common means to stop simultaneously the flow of en ergy to said discharge device from both of said circuits, said common means comprising switch means responsive to reverse current in said device to disconnect said device from said direct current circuit and relay means actuated by said switch means to impress on said control electrodes a potential negative with respect to said cathode.

2. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an arc discharge device having a cathode, a plurality of anodes and control electrodes therefor, and common means to prevent flow of energy to said device from both circuits simultaneously on occurrence of are back affecting one or more of said anodes, said means comprising a switch operable in response to reverse current in said direct current circuit to disconnect said device therefrom to prevent flow of reverse current in said anode affected by are back, and comprising means including relay means actuated by said switch to impress on said control electrodes a potential negative with respect to said cathode to prevent flow of current in said device due to the potential impressed on said plurality of anodes from said alternating current circuit.

3. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an are discharge device having a cathode and a plurality of anodes and control electrodes therefor, a switch means responsive to reverse current in said device to disconnect said device from said direct 1 current circuit upon occurrence of arc back in said device, and relay means actuated by said switch means to impress upon said control electrodes when said switch is closed a potential positive with respect to said cathode and to impress upon said control electrodes when said switch is open a potential negative with respect to said cathode.

4. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an arc discharge device having a cathode and a plurality of anodes and control electrodes therefor, a switch operable in response to reverse current in said direct current circuit to disconnect said device therefrom to prevent flow of reverse current in said device 10 due to are back, and relay means actuated by said switch, said relay means operating when said switch is closed to impress upon said control electrodes a potential positive with respect to said cathode, said relay means operating when said switch is open to impress upon said control electrodes a potential negative with respect to said cathode.

5. The combination of a direct and an alternating current circuit, means for transferring 2 power between said circuits including an are discharge device having a cathode, a plurality of anodes and control electrodes therefor, and a unitary switch means to stop simultaneously the flow of energy to said discharge device from both of said circuits, said switch means comprising a circuit breaker responsive to reverse current in said device to open said direct current circuit and a relay means mechanically actuated by said circuit breaker to impress upon said control electrodes a potential negative with respect to said cathode.

6. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an are discharge device having a cathode, a plurality of anodes and control electrodes therefor, and a unitary switch means to stop the flow of energy to said device from both circuits simultaneously upon occurrence of are back affecting one or more,

of said anodes, said unitary switch means comprising a circuit breaker operable in response to reverse current in said direct current circuit to disconnect said discharge device therefrom to prevent flow of reverse current in said anode a1- fected by arc back, and comprising relay means mechanically actuated by said circuit breaker to impress upon said control electrodes a potential negative with respect to said cathode to prevent fiow of current in said discharge device due to the potential impressed upon said plurality of anodes from said alternating current circuit.

7. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an arc v discharge device having a cathode and a plurality of anodes and control electrodes therefor, and

a unitary switch means to stop flow of energy to said device from both circuits simultaneously, said switch means comprising a circuit breaker respon- 5 sive to reverse current in said device to discon nect said device from said direct current circuit upon occurrence of are back in said device, and comprising relay means actuated by said switch means to impress upon said control electrodes 5 when said switch is closed a potential positive with respect to said cathode and to impress upon said control electrodes when said switch is open a potential negative with respect to said cathode.

8. The combination of a direct and an alternat- 7 ing current circuit, means for transferring power between said circuits including an arc discharge device having a cathode and a plurality of anodes and control electrodes therefor, and a unitary switch means to stop flow of energy to said device from both circuits simultaneously, said switch means comprising a circuit breaker operable in response to reverse current in said direct current circuit to disconnect said device therefrom to prevent flow of reverse current in said device due to arc back, and comprising relay means actuated by said circuit breaker, said relay means operating when said circuit breaker is closed to impress upon said control electrodes a potential positive with respect to said cathode, said relay means operating when said circuit breaker is open to impress upon said control electrodes a potential negative with respect to said cathode.

9. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an arc discharge device having a cathode and a plurality of anodes and control electrodes therefor, and means to stop simultaneously the flow of energy to said discharge device from both of said circuits, said means comprising a source of negative controlelectrode potential, stationary contact means connected to said source, and a circuit breaker responsive to reverse current in said device to open said direct current circuit, said breaker including a movable member provided with contact means adapted to coact with said stationary contact means to connect said control electrodes to said source of negative potential when said circuit breaker is opened.

10. The combination of a direct and an alternating current circuit, means for transferring power between said circuits including an are discharge device having a cathode and a plurality of anodes and control electrodes therefor, a source of positive control-electrode potential, a source of negative control-electrode potential, stationary contact means connected to said sources, and a circuit breaker responsive to reverse current in said device to open said direct current circuit, said breaker including a movable member provided in the closed position of said breaker to coact with certain of said stationary contact means to connect said control electrodes to said source of positive potential and in the open position of said breaker to coact with certain others of said stationary contact means to connect said control electrodes to said sources of negative potential.

DAVID C. PRINCE. 

